1. Field of the Invention
The present disclosure generally relates to an image forming apparatus, such as a copier, a facsimile, or a printer, and a process cartridge used for an image forming apparatus.
2. Description of the Background Art
Typically, an image forming apparatus using electrophotography produces an image by sequentially conducting a series of processes such as a charging process, an exposure process, a development process, a transfer process, a fixing process, and a cleaning process, for example. In the charging process, an image carrying member, such as a photoconductor, is uniformly charged. In the exposure process, an electrostatic latent image is formed on the image carrying member by scanning a light beam on the charged image carrying member. In the development process, the electrostatic latent image is developed as a toner image. In the transfer process, the toner image is transferred directly to a recording medium or indirectly transferred to a recording medium using an intermediate transfer device. In the fixing process, the toner image is fixed on the recording medium. In the cleaning process, the image carrying member is cleaned to remove residual materials, such as toner particles, remaining on the image carrying member after the transfer process. In general, such a cleaning process is conducted by using a cleaning blade, such as a rubber blade made of elastic material, in which the cleaning blade is pressed against the image carrying member to remove or scrape toner particles remaining on the image carrying member after the transfer process.
In addition to such a cleaning process using a cleaning blade, another configuration that does not use such cleaning blade has been developed as a “cleanerless system,” in which toner remaining on an image carrying member is removed and recovered after a transfer process without using a cleaning blade and a recovery system specifically used for collecting toner.
FIG. 1 illustrates an example schematic configuration of an image forming apparatus employing such a cleanerless system. As illustrated in FIG. 1, such an image forming apparatus includes a toner charge control device 105 to realize the cleanerless system, for example. The image forming apparatus further includes an image carrying member 101, a charging device 102 for charging the image carrying member 101, a development unit 106, and a transfer roller 104 for transferring a toner image from the image carrying member 101 to a transfer member 103. The toner charge control device 105 is disposed at a space between the transfer roller 104 and the charging device 102 with respect to a direction of rotation of the image carrying member 101. Specifically, the toner charge control device 105 is disposed at a downstream of the transfer roller 104 and at an upstream of the charging device 102 with respect to a direction of rotation of the image carrying member 101 as shown in FIG. 1. The toner charge control device 105 controls the polarity of charge and the charging voltage level of toner remaining on the image carrying member 101 after a transfer process. Hereinafter, the toner remaining on the image carrying member 101 after the transfer process may be referred to as “remaining toner” for the simplicity of expression.
The remaining toner is supplied with a given voltage having one polarity from the toner charge control device 105, in which the toner charge control device 105 supplies a given voltage having the same polarity as the toner. With such configuration, the polarity of charge and the charging voltage level of the remaining toner can be adjusted to a given level.
The remaining toner having the adjusted polarity and charging voltage level is then transported to a portion facing the charging device 102 by rotation of the image carrying member 101. The charging device 102, such as a fur brush roller, supplies a given bias voltage, composed of direct current having a same polarity as the toner and an alternating current superimposed to the direct current, to the remaining toner. When such bias voltage is supplied to the remaining toner, the remaining toner is separated from a surface of the image carrying member 101, and then recovered to the charging device 102.
After a given time later, the charging device 102 is set to a toner ejection mode, in which the charging device 102 is supplied with a given voltage having only direct current, so as to transfer the remaining toner, recovered in the charging device 102 as above described, to the surface of the image carrying member 101. Such transferred remaining toner is transported to a portion facing the development unit 106 with a rotation of the image carrying member 101, and is recovered into the development unit 106.
As such, a cleanerless system can reduce an amount of waste toner and can omit devices specifically used for transporting and colleting waste toner, by which an image forming apparatus can be configured with a smaller size. In such a cleanerless system, the toner charge control device 105 is used to enhance a recovery performance of remaining toner.
For example, the toner charge control device 105 may employ a conductive sheet as shown in FIG. 1, which has a relatively small and inexpensive structure. FIG. 2 illustrates an expanded view of the toner charge control device 105 employing a conductive sheet. As illustrated in FIG. 2, the toner charge control device 105 includes a conductive sheet 105a, an elastic member 105b, and a casing 110, for example. As shown in FIG. 2, one end of the conductive sheet 105a is fixed to the casing 110, and a free end portion of the conductive sheet 105a is pressed against a surface of the image carrying member 101 using the elastic member 105b that biases the conductive sheet 105a to the image carrying member 101. However, such configuration may have some drawbacks as described below.
In the configuration shown in FIG. 1, a same portion of the conductive sheet 105a may be consistently pressed to the image carrying member 101, by which the remaining toner may stick to such portion of the conductive sheet 105a. If toner sticks on the conductive sheet 105a, a charge control of remaining toner may not be conducted effectively, and resultantly, abnormal or defective image may be produced.
Further, the conductive sheet 105a may not be pressed to the image carrying member 101 with a sufficient contact area, which is needed for sufficiently controlling a polarity of charged toner and charging voltage level of charged toner. Although such charge control can be conducted by increasing a voltage supplied to the conductive sheet 105a even if the conductive sheet 105a is pressed to the image carrying member 101 with a smaller contact area, such increased voltage may cause a greater electrical stress to a photosensitive layer of the image carrying member 101, and resultantly, an abnormal or defective image may be produced.
Although such contact area of the conductive sheet 105a can be increased by some amount by increasing a size of the elastic member 105b, which presses the conductive sheet 105a, such increased contact area may cause uneven charge distribution between the conductive sheet 105a and the image carrying member 101. Further, because the free end portion of the conductive sheet 105a may not be pressed to the image carrying member 101 at a desired position easily, the image carrying member 101 and the conductive sheet 105a may not contact each other with a desired contact area.
Further, the conductive sheet 105a may be deformed when an image forming apparatus is not used for a long period of time. If such deformation occurs to the conductive sheet 105a, a contact condition of the conductive sheet 105a and the image carrying member 101 changes over time, and a charge control condition for the remaining toner may undesirably fluctuate or vary, and resultantly a lifetime of the conductive sheet 105a may be reduced. Although such deformation can be prevented by providing a deformation preventor for the conductive sheet 105a, such configuration may increase a cost and a size of an image forming apparatus.
In light of such background, a cleanerless system that effectively conducts charge control of toner remaining after a transfer process is desired. Such a cleanerless system may reduce occurrence of abnormal or defective images, and enhance a lifetime of an image forming apparatus or a process cartridge.